This invention relates generally to filters for display devices and particularly to a multicolor filter for producing purer white and for establishing uniform brightness across a display device, such as a liquid crystal display.
As is known to those skilled in the art, many display devices produce color images by passing light through filters which transmit the color of light desired for the display while filtering out other colors of light. In such devices, the color is produced by the filters rather than the elements themselves. An example of such a display device is a liquid crystal display. In liquid crystal displays, the liquid crystals are voltage actuated to change their light transmission, or reflective, capabilities to produce the desired image. As used herein, the term "transmission capabilities" also includes reflection capabilities. However, the crystals themselves do not display any color characteristics. Accordingly, when a color display is desired each crystal must be associated with an appropriate filter to produce the desired color of light. Typically, in display devices the three primary colors of red, green and blue are produced using filters, and other colors are produced by appropriately combining the various primary colors to produce the desired color. An ideal display must produce white, and for such a display the three primary colors must be produced with the proper balance of brightnesses. However, because the various colors are provided by the use of different filters, and because the filters are necessarily made of different materials, the light transmission characteristics of the three filters are different, making it extremely difficult to achieve the brightness balance needed to produce white light. In the absence of such balance the white portion of the image is tined, with the tint determined by the color filter which has the greatest light transmission capability. Typically, the color balance required for achieving white can only be obtained by lowering the transmission efficiencies of the higher transmission capability filters to substantially match the efficiency of the filter having the lowest transmission efficiency. Accordingly, for such a display the maximum brightness is determined by the transmission capability of the most inefficient color filter. This detrimentally decreases the brightness of the display produced by the display device.
In many types of liquid crystal displays the illumination is provided by backlighting the crystals. Efficiency of operation suggests that the most efficient light source be used for each backlighting. However, typically the most efficient light sources produce a high proportion of one primary color and the white light has a tint determined by that primary color. This characteristic also makes it difficult to produce flesh tones, and other colors, with a liquid crystal display. For these reasons there is a need for a multicolor filter for producing maximum and uniform brightness across a display device and for compensating for color imbalances of the illumination source. The present invention fulfills these needs.